JP7181933B2 - Adhesive film for printed wiring board - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to an adhesive film for a printed wiring board, an electromagnetic wave shielding film, and a shield wiring board.

2. Description of the Related Art In order to protect electronic circuits from electromagnetic noise, electromagnetic wave shielding films are used that are attached to printed wiring boards. The electromagnetic wave shielding film has a conductive adhesive layer and an insulating protective layer, and is adhered to the ground circuit of the printed wiring board by the conductive adhesive layer so as to be conductive.

The insulating protective layer may contain a coloring agent for the purpose of improving appearance and improving visibility of printing. For example, Patent Literature 1 attempts to improve the visibility of printing by using an insulating protective layer containing a black colorant.

JP 2016-143751 A

A printed wiring board has a base layer, a circuit pattern made of copper foil formed on the base layer, and a coverlay for protecting the circuit pattern. By attaching the electromagnetic wave shielding film to the printed wiring board, it is expected that the circuit pattern of the printed wiring board is hidden from view from the outside. In recent years, there has been a demand for thinner printed wiring boards, and there is a trend toward thinner coverlays. As the coverlay becomes thinner, the surface of the coverlay tends to have projections reflecting the circuit pattern. The inventors of the present invention have found that a conventional electromagnetic wave shielding film cannot sufficiently hide a circuit pattern when the thickness of the coverlay is reduced and the height of the protrusions is increased.

In some cases, the electromagnetic wave shielding function is not required, and the concealability of the circuit pattern is required.

An object of the present disclosure is to realize an electromagnetic wave shielding film or an attached film for a printed wiring board that has a good ability to conceal a circuit pattern even when the coverlay is thin.

One aspect of the attached film for a printed wiring board of the present disclosure includes an adhesive layer and an insulating protective layer, and the insulating protective layer has a load area ratio (Smr2) separating the protruding valley portion and the core portion from 91% or less. is.

In one aspect of the attached film for printed wiring board, the insulating protective layer may have a protrusion valley height (Svk) of 0.45 μm or more.

In one aspect of the attached film for printed wiring board, the adhesive layer has conductivity and can function as an electromagnetic wave shielding film. In this case, a shield layer may be further provided between the adhesive layer and the insulating protective layer.

One aspect of the shield wiring board of the present disclosure is a wiring board having a base layer, a circuit pattern provided on the base layer, and an insulating film adhered to the base layer so as to cover the circuit pattern, and an insulating film. and an electromagnetic shielding film of the present disclosure adhered thereon.

According to the electromagnetic wave shielding film and the printed wiring board application film of the present disclosure, even when the coverlay is thin, it is possible to greatly improve the concealability of the circuit pattern.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the adhesive film for printed wiring boards which concerns on one Embodiment. 1 is a cross-sectional view showing a shield wiring board according to one embodiment; FIG. FIG. 3 is a plan view showing a printed wiring board used for evaluation of concealability; It is a photograph which shows the observation result by a confocal microscope.

The printed wiring board adhesive film of the present embodiment is an electromagnetic wave shielding film 101 having a function as an electromagnetic wave shield, and as shown in FIG. In addition, the insulating protective layer 112 has a load area ratio (Smr2) separating the protruding valley portion and the core portion of 91% or less, preferably 90% or less. In FIG. 1, a conductive shield layer 113 is provided between the conductive adhesive layer 111 and the insulating protective layer 112. If the conductive adhesive layer 111 also functions as a shield layer, the shield A structure in which the layer 113 is not provided can be employed.

The electromagnetic wave shielding film 101 of this embodiment is adhered to the printed wiring board 102 as shown in FIG. The printed wiring board 102 includes, for example, a base layer 121, a circuit pattern 122 provided on the surface of the base layer 121, and an insulating film 124 adhered to the base layer 121 via an adhesive layer 123 so as to cover the circuit pattern 122. have.

The base layer 121 is made of an insulating material. As the insulating material, an insulating resin composition, ceramics, or the like can be used. Examples of the insulating resin composition include polyimide resins, polyamideimide resins, polyamide resins, polyetherimide resins, polyesterimide resins, polyethernitrile resins, polyethersulfone resins, polyphenylene sulfide resins, At least one selected from polyethylene terephthalate resins, polypropylene resins, crosslinked polyethylene resins, polyester resins, polybenzimidazole resins, polyimide resins, polyimideamide resins, polyetherimide resins and polyphenylene sulfide resins can be used.

The circuit pattern 122 is made of a conductive material. As the conductive material, a metal foil or a conductive material obtained by printing and curing a mixture of a conductive filler and a resin composition can be used, but from the viewpoint of cost, it is preferable to use a copper foil.

Although the thickness of the circuit pattern 122 is not particularly limited, it is preferably 1 μm to 100 μm, more preferably 1 to 50 μm. By setting the thickness of the circuit pattern to 1 μm or more, the manufacturing cost of the printed wiring board 102 can be reduced. By setting the thickness to 100 μm or less, the thickness of the printed wiring board 102 can be reduced.

The adhesive layer 123 is composed of an insulating material. As an insulating material, an insulating resin composition is preferable, and examples include polyimide resins, polyamideimide resins, polyamide resins, polyetherimide resins, polyesterimide resins, polyethernitrile resins, and polyethersulfone resins. , polyphenylene sulfide resins, polyethylene terephthalate resins, polypropylene resins, crosslinked polyethylene resins, polyester resins, polybenzimidazole resins, polyimide resins, polyimide amide resins, polyetherimide resins and polyphenylene sulfide resins At least one selected can be used.

Although the thickness of the adhesive layer 123 is not particularly limited, it is preferably 1 μm to 50 μm.

The insulating film 124 is made of an insulating material. As an insulating material, an insulating resin composition is preferable, and examples include polyimide resins, polyamideimide resins, polyamide resins, polyetherimide resins, polyesterimide resins, polyethernitrile resins, and polyethersulfone resins. , polyphenylene sulfide resins, polyethylene terephthalate resins, polypropylene resins, crosslinked polyethylene resins, polyester resins, polybenzimidazole resins, polyimide resins, polyimide amide resins, polyetherimide resins and polyphenylene sulfide resins At least one selected can be used.

Although the thickness of the insulating film 124 is not particularly limited, it is preferably 1 μm to 100 μm, more preferably 10 μm to 25 μm. By setting the thickness to 1 μm or more, the manufacturing cost of the printed wiring board 102 can be reduced. By setting the thickness to 100 μm or less, the thickness of the printed wiring board 102 can be reduced.

If the insulating protective layer 112 is colored to make the electromagnetic wave shielding film 101 opaque, the circuit pattern 122 cannot be directly viewed. For example, if the circuit pattern 122 is covered with a film having a total light transmittance of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less, the circuit pattern 122 is almost impossible to see directly. Become. However, the circuit pattern 122 forms unevenness on the surface of the insulating protective layer 112 . A general circuit pattern 122 is formed of copper lines and has a height of several μm to ten and several μm. Since the height difference between the portion where the line exists and the portion where the line does not exist becomes smaller due to the embedding of the adhesive layer 123 and the conductive adhesive layer 111, the height of the unevenness generated on the surface of the insulating protective layer 112 is several μm. However, even with such slight unevenness, the presence of the unevenness can be visually recognized on a glossy surface that easily reflects light, and the circuit pattern 122 cannot be hidden.

Therefore, in order to hide the circuit pattern 122, it is conceivable to reduce the glossiness of the surface of the insulating protective layer 112. FIG. However, the inventors of the present application have found that circuit pattern hiding power does not correlate with 85° glossiness. Glossiness is said to be greatly affected by surface roughness. It was also found that there was no correlation with the strength (Sa).

On the other hand, the concealability of the circuit pattern shows a good correlation with the load area ratio (Smr2) that separates the protruding valley and the core in accordance with International Organization for Standardization (ISO) 25178, and Smr2 is 91% or less, preferably 90%. % or less, the circuit pattern is excellent in concealability. It is believed that this is because the incident light is more likely to scatter due to the presence of a certain amount of troughs that are out of the core. Moreover, Smr2 is preferably 70% or more, more preferably 80% or more, and more preferably 85%. By setting Smr2 to 70% or more, the proportion of valleys is reduced, surface reflection at the bottom of the valleys is suppressed, and hiding properties can be improved.

In addition, since the deeper the protruding valley, the incident light is more likely to scatter, the protruding valley height Svk conforming to International Organization for Standardization (ISO) 25178 is preferably 0.45 μm or more, and more preferably 0.49 μm or more. It is preferably 0.60 μm or more, and more preferably 0.70 μm or more. Also, Svk is preferably 3.0 μm or less, more preferably 2.0 μm or less, even more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. By setting Svk to 3.0 μm or less, when the shape of the surface of the release substrate having the uneven shape is transferred to the insulating protective layer to produce an insulating protective layer having the uneven shape, the peelable group The peelability of the material from the insulating protective layer is improved.

Fine particles can be added to the resin forming the insulating protective layer 112 so that the Smr2 of the insulating protective layer 112 is 91% or less.

Although the fine particles added to the insulating protective layer 112 are not particularly limited, for example, resin fine particles or inorganic fine particles can be used. The resin fine particles may be acrylic resin fine particles, polyacrylonitrile fine particles, polyurethane fine particles, polyamide fine particles, polyimide fine particles, or the like. Inorganic fine particles include calcium carbonate fine particles, calcium silicate fine particles, clay, kaolin, talc, silica fine particles, glass fine particles, diatomaceous earth, mica powder, alumina fine particles, magnesium oxide fine particles, zinc oxide fine particles, barium sulfate fine particles, aluminum sulfate fine particles, Calcium sulfate fine particles, magnesium carbonate fine particles, and the like can be used. These resin fine particles and inorganic fine particles can be used alone or in combination.

In order to make the Smr2 of the insulating protective layer 112 91% or less, it is preferable to provide unevenness on the surface. As a method for providing unevenness on the surface, for example, the resin composition for the insulating protective layer 112 is applied to the surface of the release base material to which the unevenness is imparted by embossing or the like, and dried to form the unevenness of the release base material. is transferred to the insulating protective layer 112 . Instead of embossing, a film having a matte layer having unevenness on its surface may be used as the release substrate. The matte layer can be formed by applying a resin composition containing fine particles to the film surface or by embossing the resin layer formed on the film surface.

In addition to using a peelable substrate having unevenness, a method of applying a resin composition containing fine particles to the surface of the shield layer and drying it to form an insulating protective layer 112 having an uneven shape, A method of spraying dry ice or the like on the surface of the shield layer, a method of applying an active energy ray-curable composition to the surface of the shield layer, pressing a mold having an uneven shape to cure the curable composition layer, and peeling off the mold. method.

In addition, it is preferable to add a black colorant such as a black pigment or a mixed pigment obtained by blackening by subtractively mixing a plurality of pigments to the insulating protective layer 112 . The black pigment can be, for example, carbon black, ketjen black, carbon nanotube (CNT), perylene black, titanium black, iron black, aniline black, or the like, or a combination thereof. Mixed pigments can be used by mixing pigments such as red, green, blue, yellow, purple, cyan and magenta.

The resin component forming the insulating protective layer 112 can be, for example, a thermoplastic resin, a thermosetting resin, or an active energy ray-curable resin.

The thermoplastic resin is not particularly limited, but styrene-based resin, vinyl acetate-based resin, polyester-based resin, polyethylene-based resin, polypropylene-based resin, imide-based resin, acrylic-based resin, or the like can be used. The thermosetting resin is not particularly limited, but phenol-based resin, epoxy-based resin, urethane-based resin, melamine-based resin, polyamide-based resin, alkyd-based resin, or the like can be used. Although the active energy ray-curable resin is not particularly limited, for example, a polymerizable compound having at least two (meth)acryloyloxy groups in the molecule can be used. The insulating protective layer 112 may be made of a single material, or may be made of two or more materials. The insulating protective layer 112 can also be a laminate of two or more layers having different physical properties such as material, hardness, or elastic modulus. In this case, the Smr2 and the like on the surface of the uppermost layer may be controlled to a predetermined value.

The insulating protective layer 112 may contain a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, a viscosity At least one of a modifier, an anti-blocking agent, and the like may be included.

The thickness of the insulating protective layer 112 is not particularly limited and can be set as appropriate. Preferably, it can be 5 μm or less. By setting the thickness of the insulating protective layer 112 to 1 μm or more, the conductive adhesive layer 111 and the shield layer 113 can be sufficiently protected. By setting the thickness of the insulating protective layer 112 to 20 μm or less, the flexibility of the electromagnetic wave shielding film 101 can be ensured, and the electromagnetic wave shielding film 101 can be easily applied to members requiring flexibility.

When the shield layer 113 is provided, the shield layer 113 can be formed of a metal foil, a deposited film, a conductive filler, or the like.

The metal foil is not particularly limited, but may be nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, etc., or an alloy containing two or more of them.

Although the thickness of the metal foil is not particularly limited, it is preferably 0.5 μm or more, more preferably 1.0 μm or more. If the thickness of the metal foil is 0.5 μm or more, attenuation of high frequency signals of 10 MHz to 100 GHz transmitted to the shield printed wiring board can be suppressed. Also, the thickness of the metal foil is preferably 12 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less. Favorable elongation at break can be ensured as the thickness of the metal layer is 12 μm or less.

The deposited film is not particularly limited, but can be formed by depositing nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, and the like. Electroplating, electroless plating, sputtering, electron beam deposition, vacuum deposition, chemical vapor deposition (CVD), metal organic deposition (MOCVD), or the like can be used for vapor deposition.

The thickness of the deposited film is not particularly limited, but is preferably 0.05 μm or more, more preferably 0.1 μm or more. When the thickness of the deposited film is 0.05 μm or more, the electromagnetic wave shielding film in the shield printed wiring board has excellent properties of shielding electromagnetic waves. Also, the thickness of the deposited film is preferably less than 0.5 μm, more preferably less than 0.3 μm. When the thickness of the vapor-deposited film is less than 0.5 μm, the electromagnetic wave shielding film has excellent bending resistance, and it is possible to suppress breakage of the shield layer due to steps provided on the printed wiring board.

In the case of the conductive filler, the shield layer 113 can be formed by applying a solvent containing the conductive filler to the surface of the insulating protective layer 112 and drying it. Metal fillers, metal-coated resin fillers, carbon fillers, and mixtures thereof can be used as the conductive filler. As the metal filler, copper powder, silver powder, nickel powder, silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, gold-coated nickel powder, and the like can be used. These metal powders can be produced by an electrolysis method, an atomization method, or a reduction method. The shape of the metal powder may be spherical, flaky, fibrous, dendritic, and the like.

In this embodiment, the thickness of the shield layer 113 may be appropriately selected according to the required electromagnetic shielding effect and resistance to repeated bending and sliding. It is preferable to:

In this embodiment, the conductive adhesive layer 111 contains at least one of a thermoplastic resin thermosetting resin and an active energy ray-curable resin, and a conductive filler.

When the conductive adhesive layer 111 contains a thermoplastic resin, examples of the thermoplastic resin include styrene-based resin, vinyl acetate-based resin, polyester-based resin, polyethylene-based resin, polypropylene-based resin, imide-based resin, and acrylic-based resin. can be used. These resins may be used individually by 1 type, and may use 2 or more types together.

When the conductive adhesive layer 111 contains a thermosetting resin, the thermosetting resin includes, for example, a phenol-based resin, an epoxy-based resin, a urethane-based resin, a melamine-based resin, a polyamide-based resin, a polyimide-based resin, an alkyd-based resin, and the like. can be used. Although the active energy ray-curable resin is not particularly limited, for example, a polymerizable compound having at least two (meth)acryloyloxy groups in the molecule can be used. These resins may be used individually by 1 type, and may use 2 or more types together.

The thermosetting resin includes, for example, a first resin component having a reactive first functional group and a second resin component that reacts with the first functional group. The first functional group can be, for example, an epoxy group, an amide group, or a hydroxyl group. The second functional group may be selected according to the first functional group. For example, when the first functional group is an epoxy group, it can be a hydroxyl group, a carboxyl group, an epoxy group, an amino group, or the like. Specifically, for example, when the first resin component is an epoxy resin, the second resin component is an epoxy group-modified polyester resin, an epoxy group-modified polyamide resin, an epoxy group-modified acrylic resin, an epoxy group-modified polyurethane polyurea resin, a carboxyl Group-modified polyester resins, carboxyl group-modified polyamide resins, carboxyl group-modified acrylic resins, carboxyl group-modified polyurethane polyurea resins, urethane-modified polyester resins, and the like can be used. Among these, carboxyl group-modified polyester resins, carboxyl group-modified polyamide resins, carboxyl group-modified polyurethane polyurea resins, and urethane-modified polyester resins are preferred. Further, when the first resin component is a hydroxyl group, the second resin component includes an epoxy group-modified polyester resin, an epoxy group-modified polyamide resin, an epoxy group-modified acrylic resin, an epoxy group-modified polyurethane polyurea resin, a carboxyl group-modified polyester resin, Carboxyl group-modified polyamide resins, carboxyl group-modified acrylic resins, carboxyl group-modified polyurethane polyurea resins, urethane-modified polyester resins, and the like can be used. Among these, carboxyl group-modified polyester resins, carboxyl group-modified polyamide resins, carboxyl group-modified polyurethane polyurea resins, and urethane-modified polyester resins are preferred.

The thermosetting resin may contain a curing agent that accelerates the thermosetting reaction. When the thermosetting resin has a first functional group and a second functional group, the curing agent can be appropriately selected according to the types of the first functional group and the second functional group. When the first functional group is an epoxy group and the second functional group is a hydroxyl group, imidazole curing agents, phenolic curing agents, cationic curing agents, and the like can be used. These can also be used individually by 1 type, and can also use 2 or more types together. In addition, optional components such as antifoaming agents, antioxidants, viscosity modifiers, diluents, anti-settling agents, leveling agents, coupling agents, colorants, and flame retardants may be included.

The conductive filler is not particularly limited, but metal fillers, metal-coated resin fillers, carbon fillers, and mixtures thereof can be used, for example. Examples of metal fillers include copper powder, silver powder, nickel powder, silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder. These metal powders can be produced by an electrolysis method, an atomization method, a reduction method, or the like. Among them, silver powder, silver-coated copper powder and copper powder are preferable.

The conductive filler preferably has an average particle size of 1 µm or more, more preferably 3 µm or more, preferably 50 µm or less, and more preferably 40 µm or less, from the viewpoint of contact between fillers. The shape of the conductive filler is not particularly limited, and may be spherical, flaky, dendritic, fibrous, or the like.

The content of the conductive filler can be appropriately selected depending on the application. It is 90% by mass or less. From the viewpoint of embeddability, it is preferably 70% by mass or less, more preferably 60% by mass or less. Moreover, when realizing anisotropic conductivity, the content is preferably 40% by mass or less, more preferably 35% by mass or less.

The thickness of the conductive adhesive layer 111 is preferably 1 μm to 50 μm from the viewpoint of embedding.

The conductive adhesive layer 111 can also be a layer having a so-called adhesive property, which has tackiness in an environment of normal temperature (for example, 20° C.). Since the conductive adhesive layer 111 has tackiness in a room temperature environment, the electromagnetic wave shielding film 101 can be easily attached to any position on the printed wiring board 102 .

When the electromagnetic wave shielding film 101 has the shield layer 113 made of metal foil or the like, the total light transmittance is usually almost zero. When the shield layer 113 is not provided, the total light transmittance is preferably adjusted to 20% by adjusting the amount of coloring agents, fillers, etc. added to the insulating protective layer 112 and/or the conductive adhesive layer 111. Below, it is more preferably 10% or less, still more preferably 5% or less. By setting the total light transmittance to 20% or less, when the electromagnetic wave shielding film 101 is attached to the printed wiring board 102, the circuit pattern 122 can be made difficult to be directly visually recognized. The total light transmittance can be measured according to JIS K7136.

In the present embodiment, an example in which the printed wiring board adhesive film is an electromagnetic wave shielding film is shown, but it is also possible to use a printed wiring board adhesive film that does not have an electromagnetic wave shielding function. In this case, a non-conductive adhesive layer containing no conductive filler can be used instead of the conductive adhesive layer. If the electromagnetic wave shielding function is not required, the shield layer need not be provided. However, a metal foil or the like may be provided between the adhesive layer and the insulating protective layer in order to lower the total light transmittance.

Below, the printed wiring board sticking film of the present disclosure will be described in further detail using examples. The following examples are illustrative and not intended to limit the invention.

<Preparation of peelable substrate>
Dry ice particles were sprayed on the surface of a polyethylene terephthalate film (hereinafter referred to as a PET film) having a thickness of 25 μm to form unevenness, and then a release layer made of a melamine resin was provided to obtain a release substrate 1 .

A matte layer composition comprising silica particles, melamine resin, and toluene is prepared, applied to the surface of a polyethylene terephthalate film having a thickness of 25 μm using a wire bar, and dried by heating to form a matte layer having a thickness of 5 μm. A flexible substrate 2 was obtained. Release substrates 3 to 9 having different surface states were obtained in the same manner by changing the particle size and amount of silica particles added. Table 1 summarizes the surface properties of the surfaces of the peelable substrates 1 to 9 (surfaces on which the concealing layers are formed).

<Preparation of insulating protective layer>
So that the solid content is 20% by mass, 100 parts by mass of bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical, jER1256) in toluene, 0.1 part by mass of (Mitsubishi Chemical, ST14) as a curing agent, black color 15 parts by mass of carbon particles (TOKA BLACK #8300/F manufactured by Tokai Carbon Co., Ltd.) were mixed as a coloring agent to prepare a resin composition for an insulating protective layer. This composition was applied to the surface of the peelable substrate using a wire bar and dried by heating to form an insulating protective layer having a thickness of 5 μm on the surface of the peelable substrate. Next, a 0.1 μm thick Ag deposition film was formed as a shield layer on the protective layer.

<Preparation of adhesive layer>
100 parts by mass of bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical, jER1256), 0.1 part by mass of a curing agent (manufactured by Mitsubishi Chemical, ST14) in toluene so that the solid content is 20% by mass, and the average particle size 30 parts by mass of 15 μm dendritic silver-coated copper powder was added and mixed with stirring to prepare an adhesive layer composition. The resulting adhesive layer composition was applied to a PET film (hereinafter referred to as a support film) whose surface had been subjected to release treatment using a wire bar and dried by heating to form an adhesive layer having a thickness of 5 μm on the surface of the support film. formed.

<Preparation of film attached to printed wiring board>
The surface of the insulating protective layer formed on the surface of the peelable base material on the side of the Ag vapor deposition film and the adhesive layer formed on the surface of the support film are laminated together, and a pair of metal rolls heated to 100° C. are used. and pressurized at a pressure of 5 MPa to obtain a film attached to a printed wiring board, which is an electromagnetic wave shielding film.

<Creation of shield wiring board>
The obtained printed wiring board sticking film and the printed wiring board are adhered using a press under the conditions of temperature: 170 ° C., time: 3 minutes, pressure: 2 to 3 MPa, and then the peelable substrate is peeled off to shield. I made a wiring board.

A printed wiring board was used in which a circuit pattern 122 as shown in FIG. 4 was formed on a base layer 121 made of a polyimide film. The circuit pattern 122 was made of copper foil with a line width of 0.1 mm and a height of 12 μm. An adhesive layer with a thickness of 25 μm and a coverlay (insulating film) made of a polyimide film with a thickness of 12.5 μm were provided on the base layer 121 so as to cover the circuit pattern 122 .

<Measurement of glossiness>
The 85° gloss was measured according to JIS Z 8741 using a portable gloss meter (BYK Gardner Micro-Gloss, Toyo Seiki Seisakusho).

<Measurement of surface roughness>
Using a confocal microscope (manufactured by Lasertec, OPTELICS HYBRID, 20x objective lens), any five points on the surface were measured according to ISO25178. After that, surface tilt correction was performed using data analysis software (LMeye7), and Smr2, Svk and Sa were measured. The cutoff wavelength of the S filter was set to 0.0025 mm, and the cutoff wavelength of the L filter was set to 0.8 mm. Each numerical value is the average value of the values obtained by measuring five arbitrary points on the surface.

<Evaluation of Concealability>
Place the shield wiring board on a flat table surface, under an environment where the illuminance of the surface of the shield wiring board is 500 lux, the height from the shield wiring board is 30 cm, at an angle of 45 degrees, from the insulating protective layer side It was evaluated whether the circuit pattern was visible. The case where the circuit pattern was not visible was evaluated as good (○), and the case where the circuit pattern was visible was evaluated as poor (X).

(Example 1)
A film attached to a printed wiring board was prepared from an insulating protective layer formed using the peelable base material 1 to obtain a shield wiring board. The insulating protective layer of the shield wiring board after removing the peelable base material had an Smr2 of 90.1% and an Svk of 0.62 μm. The 85° glossiness was 33.7 and Sa was 0.48 μm. In a visual inspection, the circuit pattern could not be visually recognized, and the hiding property was very good. Even in observation with a confocal microscope, the circuit pattern was hardly visible.

(Example 2)
A shield wiring board was obtained in the same manner as in Example 1, except that the peelable base material 2 was used. The insulating protective layer of the shield wiring board after removing the peelable base material had an Smr2 of 90.8% and an Svk of 0.55 μm. The 85° glossiness was 28.7 and Sa was 0.41 µm. In a visual inspection, the circuit pattern could not be visually recognized, and the hiding property was very good. Even in observation with a confocal microscope, the circuit pattern was hardly visible.

(Example 3)
A shield wiring board was obtained in the same manner as in Example 1, except that the peelable base material 3 was used. The insulating protective layer of the shield wiring board after removing the peelable base material had an Smr2 of 90.0% and an Svk of 0.71 μm. The 85° glossiness was 32.3 and Sa was 0.51 μm. In a visual inspection, the circuit pattern could not be visually recognized, and the hiding property was very good. Even in observation with a confocal microscope, the circuit pattern was hardly visible.

(Example 4)
A shield wiring board was obtained in the same manner as in Example 1, except that the peelable base material 4 was used. The insulating protective layer of the shield wiring board after removing the peelable base material had an Smr2 of 89.6% and an Svk of 0.49 μm. The 85° glossiness was 41.1 and Sa was 0.42 μm. In visual inspection, the circuit pattern could not be visually recognized, and the hiding property was good. In observation with a confocal microscope, the circuit pattern was slightly visible.

(Example 5)
A shield wiring board was obtained in the same manner as in Example 1 except that the peelable base material 5 was used. After removing the peelable base material, the insulating protective layer of the shield wiring board had an Smr2 of 90.8% and an Svk of 0.90 μm. The 85° glossiness was 12.6 and Sa was 0.83 μm. In a visual inspection, the circuit pattern could not be visually recognized, and the hiding property was very good. Even in observation with a confocal microscope, the circuit pattern was hardly visible.

(Example 6)
A shield wiring board was obtained in the same manner as in Example 1 except that the peelable base material 6 was used. The insulating protective layer of the shield wiring board after removing the peelable base material had an Smr2 of 89.1% and an Svk of 0.63 μm. The 85° glossiness was 30.0 and Sa was 0.47 μm. In a visual inspection, the circuit pattern could not be visually recognized, and the hiding property was very good. Even in observation with a confocal microscope, the circuit pattern was hardly visible.

(Comparative example 1)
A shield wiring board was obtained in the same manner as in Example 1 except that the peelable base material 7 was used. The insulating protective layer of the shield wiring board after removing the peelable base material had an Smr2 of 92.1% and an Svk of 0.39 μm. The 85° glossiness was 30.6 and Sa was 0.45 μm. By visual inspection, the circuit pattern could be visually recognized, and the hiding property was poor. The circuit pattern was clearly visible in observation with a confocal microscope.

(Comparative example 2)
A shield wiring board was obtained in the same manner as in Example 1 except that the peelable base material 8 was used. After removing the peelable base material, the insulating protective layer of the shield wiring board had an Smr2 of 93.9% and an Svk of 0.29 μm. The 85° glossiness was 39.9 and Sa was 0.43 μm. By visual inspection, the circuit pattern could be visually recognized, and the hiding property was poor. The circuit pattern was clearly visible in observation with a confocal microscope.

(Comparative Example 3)
A shield wiring board was obtained in the same manner as in Example 1 except that the peelable base material 9 was used. The insulating protective layer of the shield wiring board after removing the peelable base material had an Smr2 of 92.8% and an Svk of 0.43 μm. The 85° glossiness was 37.0 and Sa was 0.45 μm. By visual inspection, the circuit pattern could be visually recognized, and the hiding property was poor. The circuit pattern was clearly visible in observation with a confocal microscope.

Table 2 shows the properties of the insulating protective layer and the circuit pattern concealability of each example and comparative example. When Smr2 was 91 or less, the hiding property was good.

FIG. 4 shows the results of observation by a confocal microscope in each example and comparative example. In each example, the shape of the circuit pattern could hardly be recognized, whereas in each comparative example, the shape of the circuit pattern could be clearly recognized.

The electromagnetic wave shielding film and the film attached to a printed wiring board according to the present disclosure are excellent in concealability, and are useful in applications where concealment of circuit patterns is required.

101 electromagnetic wave shielding film 102 printed wiring board 111 conductive adhesive layer 112 insulating protective layer 113 shield layer 121 base layer 122 circuit pattern 123 adhesive layer 124 insulating film

Claims (5)

An adhesive layer and an insulating protective layer,
The insulating protective layer has a load area ratio (Smr2) separating the projecting valley and the core of 91% or less, and the insulating protective layer has a projecting valley height (Svk) of 0.45 μm or more. , adhesive film for printed wiring boards. An adhesive layer and an insulating protective layer,
The adhesive film for a printed wiring board, wherein the insulating protective layer is opaque, and has a load area ratio (Smr2) separating the projecting valley portion and the core portion of 91% or less. The attached film for a printed wiring board according to claim 1 or 2, wherein the adhesive layer has conductivity and functions as an electromagnetic wave shielding film. 4. The adhesive film for printed wiring board according to claim 3, further comprising a shield layer between said adhesive layer and said insulating protective layer. a wiring board having a base layer, a circuit pattern provided on the base layer, and an insulating film adhered to the base layer so as to cover the circuit pattern;
5. A shield wiring board comprising the printed wiring board sticking film according to claim 3 or 4 adhered on the insulating film.

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